A passive optical network (PON) technology is currently a main broadband access technology. A conventional PON system is a point-to-multipoint network system based on a time division multiplexing (Time Division Multiplexing, TDM) mechanism. Referring to FIG. 1, the PON system generally includes an optical line terminal (Optical Line Terminal, OLT) located on a central office side, multiple optical network units (Optical Network Unit, ONU) located on a user side, and an optical distribution network (Optical Distribution Network, ODN) between the OLT and the ONUs. The ODN is used to distribute or multiplex data signals between the OLT and the ONUs so that the multiple ONUs can share an optical transmission path. In the PON system based on the TDM mechanism, a direction from the OLT to the ONUs is called downstream, the OLT broadcasts a downstream data stream to all the ONUs in a TDM manner, and each ONU receives only the data that carries an identifier of the ONU; a direction from the ONUs to the OLT is called upstream. Because all the ONUs share the optical transmission path, in order to prevent a conflict of upstream data between the ONUs, the PON system uses a Time Division Multiple Access (Time Division Multiple Access, TDMA) manner in the upstream direction. That is, the OLT allocates a timeslot to each ONU, and each ONU sends upstream data in strict accordance with the timeslot allocated by the OLT.
However, the PON system is affected by a time division characteristic of the TDM mechanism, and available bandwidth of a user is generally restricted. In addition, available bandwidth of a fiber itself cannot be effectively used. Therefore, emerging broadband network application service requirements cannot be satisfied. To solve such a problem and in view of compatibility with an existing PON system, a hybrid PON system that integrates a wavelength division multiplexing (Wavelength Division Multiplexing, WDM) technology and the TDM technology is put forward in the industry. In the hybrid PON, multiple wavelength channels are used between an OLT on a central office side and ONUs on a user side to receive and send data. That is, the hybrid PON system is a multi-wavelength PON system.
In the multi-wavelength PON system, the OLT supports data sending and receiving performed simultaneously by using multiple wavelength channels. Each ONU works on one of the wavelength channels separately. In the downstream direction, the OLT uses a downstream wavelength corresponding to each wavelength channel to broadcast downstream data to multiple ONUs that work on the wavelength channel; in the upstream direction, an ONU on each wavelength channel may, in a timeslot allocated by the OLT, send upstream data to the OLT by using an upstream wavelength of the wavelength channel To reduce warehousing costs, the ONU generally uses a wavelength-tunable optical transceiver component. Therefore, during initialization, the ONU needs to negotiate with the OLT to agree on a pair of working wavelengths by means of wavelength negotiation.
In the existing multi-wavelength PON system, in a wavelength negotiation process during initialization of the ONU, the ONU generally selects working wavelengths at random, and then the OLT detects whether a wavelength conflict occurs between the working wavelengths selected by the ONU and those of other ONUs. If the wavelength conflict occurs, the OLT delivers a conflict indication to the ONU. After receiving the conflict indication, the ONU selects other working wavelengths after a random delay. However, the foregoing method completely depends on that the ONU selects the wavelengths by itself and negotiates with the OLT, and, if a wavelength conflict occurs, new wavelengths are selected for negotiation, which leads to long registration time of the ONU and may interfere with normal communication of the other ONUs.